Abstract

Background

The role of lateral gene transfer (LGT) in the evolution of microorganisms is only
beginning to be understood. While most LGT events occur between closely related individuals,
inter-phylum and inter-domain LGT events are not uncommon. These distant transfer
events offer potentially greater fitness advantages and it is for this reason that
these "long distance" LGT events may have significantly impacted the evolution of
microbes. One mechanism driving distant LGT events is microbial transformation. Theoretically,
transformative events can occur between any two species provided that the DNA of one
enters the habitat of the other. Two categories of microorganisms that are well-known
for LGT are the thermophiles and halophiles.

Results

We identified potential inter-class LGT events into both a thermophilic class of Archaea
(Thermoprotei) and a halophilic class of Archaea (Halobacteria). We then categorized
these LGT genes as originating in thermophiles and halophiles respectively. While
more than 68% of transfer events into Thermoprotei taxa originated in other thermophiles,
less than 11% of transfer events into Halobacteria taxa originated in other halophiles.

Conclusions

Our results suggest that there is a fundamental difference between LGT in thermophiles
and halophiles. We theorize that the difference lies in the different natures of the
environments. While DNA degrades rapidly in thermal environments due to temperature-driven
denaturization, hypersaline environments are adept at preserving DNA. Furthermore,
most hypersaline environments, as topographical minima, are natural collectors of
cellular debris. Thus halophiles would in theory be exposed to a greater diversity
and quantity of extracellular DNA than thermophiles.